So she and I had two questions that we never resolved. First, is it really true that hitting the "Spam" button on a site like Yahoo or Gmail informs the sender of your email address? (Doesn't this lead to the usual concerns about confirming a valid address?) And second, what is a user supposed to do in the case of an accidental bump of the "Spam" button? Is there really no way to undo the damage (both to the sender and to the willing recipient)?
Yes. The feedback loop shows the sender who marked the mail as spam.
> What is a user supposed to do in the case of an accidental bump of the "Spam" button? Is there really no way to undo the damage (both to the sender and to the willing recipient)?
There is no good solution, it kind of sucks for both the sender and the receiver. When you click that spam button, intentional or not, I can no longer send you email until going through a sometimes laborious process of working with the email service to get the email unblacklisted. If you really want to receive email again, send an email to the company/person and let them know you accidentally clicked the spam button so they can work it out with the email provider.
Gmail handles this the best IMO as it gives the user ~5 seconds to click "undo" before reporting the spam. As far as I can tell most other email clients are instantaneous.
I think the fear of "confirming an email address is valid" is unfounded. A list of valid email addresses of people who actively report messages they don't want as spam is not worth anything to a spammer and it would be illegal for a US company to do anything with the list of unsubscribes or spam reports anyway.
I'm not aware of any simple and universal solution to "undo" an accidental spam button click.
But if we're talking about newsletters your don't remember signing up for or marketing emails or invites to a new social network, the unsubscribe usually works and will almost never harm you. AFAIK it's a myth that there's this huge black market for "valid" email addresses. Spammers don't want a list of people who click unsubscribe; they ain't gonna buy anything. There are way easier ways to find email addresses on the internet. And it would be crazy (and possibly illegal) for any sort of semi-legit company to sell their unsubscribe list.
Anything send by an actual company -- especially anything sent through any of the major email providers -- will almost certainly have a working unsubscribe. It's almost impossible to send a message in MailChimp without a working unsubscribe.
I routinely deal with people complaining about not getting a newsletter they requested after they marked it as spam (once they do that, we are required by agreement with the ISP to not send them any more messages ever).